U.S. patent application number 15/361539 was filed with the patent office on 2017-12-14 for carrier including ammonium oxidizing bacteria immobilized therein and method for preparing same.
This patent application is currently assigned to KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. The applicant listed for this patent is KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to Hyokwan BAE, Dae Hee CHOI, Yunchul CHUNG, Jin Young JUNG, Dong Ryeol LEE, Seockheon LEE.
Application Number | 20170355979 15/361539 |
Document ID | / |
Family ID | 60572330 |
Filed Date | 2017-12-14 |
United States Patent
Application |
20170355979 |
Kind Code |
A1 |
BAE; Hyokwan ; et
al. |
December 14, 2017 |
CARRIER INCLUDING AMMONIUM OXIDIZING BACTERIA IMMOBILIZED THEREIN
AND METHOD FOR PREPARING SAME
Abstract
Disclosed is a method for preparing the same. The method for
preparing a carrier including ammonium oxidizing bacteria
immobilized therein includes: preparing a PVA-alginate mixed
solution containing PVA mixed with alginate; adding sludge
containing ammonium oxidizing bacteria and sodium bicarbonate
(NaHCO.sub.3) to the PVA-alginate mixed solution to obtain a
foaming-beading solution; and dropping the foaming-beading solution
to a saturated boric acid solution to obtain beads including sludge
immobilized therein, wherein sodium bicarbonate (NaHCO.sub.3) is
decomposed to produce carbon dioxide (CO.sub.2) which is discharged
to the exterior of the beads to form pores in the beads, when the
foaming-beading solution is dropped to the saturated boric acid
solution to obtain beads including sludge immobilized therein.
Inventors: |
BAE; Hyokwan; (Seoul,
KR) ; LEE; Seockheon; (Seoul, KR) ; CHUNG;
Yunchul; (Seoul, KR) ; JUNG; Jin Young;
(Daegu, KR) ; CHOI; Dae Hee; (Daegu, KR) ;
LEE; Dong Ryeol; (Daegu, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY |
Seoul |
|
KR |
|
|
Assignee: |
KOREA INSTITUTE OF SCIENCE AND
TECHNOLOGY
Seoul
KR
|
Family ID: |
60572330 |
Appl. No.: |
15/361539 |
Filed: |
November 28, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C12N 11/04 20130101;
C12N 11/10 20130101; C02F 3/106 20130101; C02F 3/302 20130101; C02F
3/307 20130101; C02F 2101/16 20130101; Y02W 10/15 20150501; C12N
11/08 20130101; C02F 3/104 20130101; C02F 3/303 20130101; C02F
3/2806 20130101; C02F 3/108 20130101; C02F 3/348 20130101; Y02W
10/10 20150501; C02F 3/107 20130101 |
International
Class: |
C12N 11/10 20060101
C12N011/10; C02F 3/28 20060101 C02F003/28; C02F 3/10 20060101
C02F003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2016 |
KR |
10-2016-0073109 |
Claims
1. A method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein, which comprises: preparing a
PVA-alginate mixed solution containing PVA mixed with alginate;
adding sludge containing ammonium oxidizing bacteria and sodium
bicarbonate (NaHCO.sub.3) to the PVA-alginate mixed solution to
obtain a foaming-beading solution; and dropping the foaming-beading
solution to a saturated boric acid solution to obtain beads
including sludge immobilized therein, wherein sodium bicarbonate
(NaHCO.sub.3) is decomposed to produce carbon dioxide (CO.sub.2)
which is discharged to the exterior of the beads to form pores in
the beads, when the foaming-beading solution is dropped to the
saturated boric acid solution to obtain beads including sludge
immobilized therein.
2. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 1, wherein the
foaming-beading solution comprises sodium bicarbonate (NaHCO.sub.3)
in an amount of 0.15-1.2% (w/v).
3. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 1, wherein the
foaming-beading solution comprises sodium bicarbonate (NaHCO.sub.3)
in an amount of 0.5-0.7% (w/v).
4. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 1, which further
comprises dipping the beads including the beads immobilized therein
in a phosphoric acid solution to increase the mechanical
strength.
5. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 1, wherein the
foaming-beading solution comprises zeolite, and the zeolite is
provided in the beads comprising the sludge immobilized
therein.
6. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 1, wherein the
saturated boric acid solution is controlled to have a pH of
3-4.
7. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 1, which further
comprises dipping the beads comprising the sludge immobilized
therein in distilled water to induce swelling of the beads so that
sodium bicarbonate (NaHCO.sub.3) and unreacted alginate remaining
in the beads may be discharged to the exterior of the beads.
8. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 1, wherein the
foaming-beading solution comprises solid particles, and the solid
particles are detached from the beads to form pores, after the
beads including the sludge immobilized therein are obtained.
9. The method for preparing a carrier comprising ammonium oxidizing
bacteria immobilized therein according to claim 8, wherein the
solid particle is activated carbon.
10. The method for preparing a carrier comprising ammonium
oxidizing bacteria immobilized therein according to claim 1,
wherein the ammonium oxidizing bacteria comprise at least one
selected from a group comprising anaerobic ammonium oxidizing
bacteria and aerobic ammonium oxidizing bacteria.
11. The method for preparing a carrier comprising ammonium
oxidizing bacteria immobilized therein according to claim 10,
wherein heterotrophic denitrifying bacteria is used to remove
nitrite or nitrate in the form of dinitrogen gas.
12. A carrier comprising ammonium oxidizing bacteria immobilized
therein obtained by the method as defined in claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Korean Patent
Application No. 10-2016-0073109, filed on Jun. 13, 2016, and all
the benefits accruing therefrom under 35 U.S.C. .sctn.119, the
contents of which in its entirety are herein incorporated by
reference.
BACKGROUND
1. Field
[0002] The present disclosure relates to a carrier including
ammonium oxidizing bacteria immobilized therein and a method for
preparing the same. More particularly, the present disclosure
relates to a carrier including ammonium oxidizing bacteria
immobilized therein, which is obtained by converting sludge
containing anaerobic ammonium oxidizing bacteria or aerobic
ammonium oxidizing bacteria into beads and is capable of improving
gas permeability and strength, and a method for preparing the
same.
2. Description of the Related Art
[0003] As a method for removing nitrogen in sewage and wastewater,
a biological process based on nitrification and heterotrophic
denitrification has been used widely. According to the conventional
biological process, nitrification is carried out by oxidation of
ammonia and oxidation of nitrite sequentially. Herein, when
oxidizing nitrogen through oxidation of ammonia and oxidation of
nitrite, a large amount of oxygen is required. In addition,
heterotrophic denitrification in a biological process requires
supply of an organic carbon source as an electron donor of bacteria
in order to reduce nitrite or nitrate. Although relatively
inexpensive methanol has been used generally as an organic carbon
source, continuous supply of methanol is required, and thus there
is a burden on operation cost.
[0004] To solve such a problem of a biological process, many
studies have been conducted recently about a method for removing
nitrogen by using anaerobic ammonium oxidizing bacteria (see,
Korean Patent Publication No. 10-1040518). Anaerobic ammonium
oxidizing bacteria are autotrophic bacteria using ammonium
(NH.sub.4.sup.+) and nitrite (NO.sub.2.sup.-) as substrates to
produce dinitrogen gas (N.sub.2) under an anaerobic condition.
Since anaerobic ammonium oxidizing bacteria use ammonium
(NH.sub.4.sup.+) as an electron donor and nitrite (NO.sub.2.sup.-)
as an electron acceptor, there is no need for addition of an
organic carbon source, unlike the conventional biological process.
In addition, there is an advantage in that the amount of oxygen
required for partial nitrification of ammoniacal nitrogen is
reduced by about 40% as compared to the conventional biological
process, and thus the cost required for aeration and carbon source
supply is saved.
[0005] In addition, an autotrophic denitrification process using
anaerobic ammonium oxidizing bacteria shows significantly higher
denitrification efficiency of 26-42 kgN/m.sup.3day, as compared to
the conventional biological process which provides the maximum
heterotrophic denitrification efficiency of at most 3
kgN/m.sup.3day.
[0006] Meanwhile, five major genera of anaerobic ammonium oxidizing
bacteria, Candidatus Brocadia, Candidatus Kuenenia, Candidatus
Scalindua, Candidatus Anammoxoglobus and Candidatus Jettenia, have
been found in wastewater treatment processes and natural
environments, and they characteristically show a very low growth
rate, i.e., a doubling time of about 11 days. Thus, it is reported
that a long start-up period is required to allow autotrophic
denitrification based on anaerobic ammonium oxidizing bacteria to
proceed to a predetermined level, and continuous additional
introduction of anaerobic ammonium oxidizing bacteria for at least
1 year is required after the anaerobic ammonium oxidizing bacteria
are applied first (Van der Star W R, Abma W R, Blommers D, Mulder J
W, Tokutomi T, Strous M, Picioreanu C, van Loosdrecht M C (2007)
Startup of reactors for anoxic ammonium oxidation: experiences from
the first full-scale anammox reactor in Rotterdam. Water Research
41:4149-4163). For reference, aerobic ammonium oxidizing bacteria
show a doubling time of 8 hours, which is faster than the growth
rate of anaerobic ammonium oxidizing bacteria but significantly
slower than the general aerobic bacteria.
[0007] The start-up period of an anaerobic ammonium oxidation
process is affected by the configuration of a reactor, quality of
influent, stability of process conditions, or the like. Among
those, the most important factor is immobilization technology for
retaining anaerobic ammonium oxidizing bacteria in a reactor.
Currently, the most widely used immobilization technology is a
method for accelerating aggregation to induce granulation. However,
it is required to maintain a significantly complicated operating
condition to carry out aggregation of bacteria. In addition, after
the lapse of 3-6 months required for aggregation, additional cost
and time are required to increase the amount of aggregated granular
sludge. Thus, it is not adequate to obtain a large amount of
anaerobic ammonium oxidizing bacteria at an early stage.
[0008] More recently, a method for immobilizing anaerobic ammonium
oxidizing bacteria by using a synthetic polymer has been suggested.
The present applicant has suggested a method for cultivating
anaerobic ammonium oxidizing bacteria by converting active sludge
containing anaerobic ammonium oxidizing bacteria into beads through
Korean Patent Application No. 10-2014-185833.
[0009] One of the factors to be considered when immobilizing
anaerobic ammonium oxidizing bacteria by using a synthetic polymer,
such as poly(vinyl alcohol) (PVA), is the gas permeability and
strength of a carrier.
[0010] The anaerobic ammonium oxidizing bacteria immobilized in a
carrier produce dinitrogen gas (N.sub.2) while they are grown with
ammonium and nitrite as substrates. It is required to discharge the
produced dinitrogen gas smoothly to the exterior. When such
dinitrogen gas is not discharged, the carrier may be swelled and
broken. To discharge such dinitrogen gas smoothly, it is required
for the carrier to have pores by which the inner part and outer
part of the carrier are connected spatially with each other. In
addition, the carrier including anaerobic ammonium bacteria
immobilized therein should have high physical strength, because
they are used for a long time in the reactor.
REFERENCES
Patent Documents
[0011] Korean Patent Publication No. 1040518
Non-Patent Documents
[0012] Van der Star W R, Abma W R, Blommers D, Mulder J W, Tokutomi
T, Strous M, Picioreanu C, van Loosdrecht M C (2007) Startup of
reactors for anoxic ammonium oxidation: experiences from the first
full-scale anammox reactor in Rotterdam. Water Research
41:4149-4163.
SUMMARY
[0013] The present disclosure is directed to providing a carrier
including ammonium oxidizing bacteria immobilized therein, which is
obtained by converting sludge containing anaerobic ammonium
oxidizing bacteria or aerobic ammonium oxidizing bacteria into
beads and is capable of improving gas permeability and strength,
and a method for preparing the same.
[0014] In one aspect, there is provided a method for preparing a
carrier including ammonium oxidizing bacteria immobilized therein,
which includes: preparing a PVA-alginate mixed solution containing
PVA mixed with alginate; adding sludge containing ammonium
oxidizing bacteria and sodium bicarbonate (NaHCO.sub.3) to the
PVA-alginate mixed solution to obtain a foaming-beading solution;
and dropping the foaming-beading solution to a saturated boric acid
solution to obtain beads including sludge immobilized therein,
wherein sodium bicarbonate (NaHCO.sub.3) is decomposed to produce
carbon dioxide (CO.sub.2) which is discharged to the exterior of
the beads to form pores in the beads, when the foaming-beading
solution is dropped to the saturated boric acid solution to obtain
beads including sludge immobilized therein.
[0015] According to an embodiment, the foaming-beading solution may
include sodium bicarbonate (NaHCO.sub.3) in an amount of 0.15-1.2%
(w/v), particularly 0.5-0.7% (w/v).
[0016] According to another embodiment, the method may further
include dipping the beads including the beads immobilized therein
in a phosphoric acid solution to increase the mechanical
strength.
[0017] According to still another embodiment, the foaming-beading
solution may include zeolite, and the zeolite may be provided in
the beads including the sludge immobilized therein.
[0018] According to still another embodiment, the saturated boric
acid solution may be controlled to have a pH of 3-4.
[0019] According to still another embodiment, the method may
further include dipping the beads including the sludge immobilized
therein in distilled water to induce swelling of the beads so that
sodium bicarbonate (NaHCO.sub.3) and unreacted alginate remaining
in the beads may be discharged to the exterior of the beads.
[0020] According to still another embodiment, the foaming-beading
solution may include solid particles, and the solid particles may
be detached from the beads to form pores, after the beads including
the sludge immobilized therein are obtained. The solid particles
may be activated carbon.
[0021] According to yet another embodiment, the ammonium oxidizing
bacteria may comprise at least one selected from a group comprising
anaerobic ammonium oxidizing bacteria and aerobic ammonium
oxidizing bacteria.
[0022] Alternatively, for the purpose of heterotrophic
denitrification, heterotrophic denitrifying bacteria can be used
instead of the ammonium oxidizing bacteria in order to remove
nitrite or nitrate in the form of dinitrogen gas.
[0023] The carrier including ammonium oxidizing bacteria
immobilized therein and the method for preparing the same provide
the following effect.
[0024] Since sodium bicarbonate (NaHCO.sub.3) is used when
immobilizing ammonium oxidizing bacteria in PVA-alginate based
beads, it is possible to improve the gas permeability and strength
of the beads.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a flow chart illustrating the method for preparing
a carrier including ammonium oxidizing bacteria immobilized therein
according to an embodiment of the present disclosure.
[0026] FIG. 2 is a schematic view illustrating the method for
preparing a carrier including ammonium oxidizing bacteria
immobilized therein according to an embodiment of the present
disclosure.
[0027] FIG. 3 is a scanning electron microscopic (SEM) image of the
beads obtained according to Test Example 1.
[0028] FIG. 4 shows the test results illustrating the porosity of
the beads obtained according to Test Example 1.
[0029] FIG. 5 shows the test results illustrating the density of
the beads obtained according to Test Example 1.
[0030] FIG. 6 shows the test results illustrating the swelling
degree of the beads obtained according to Test Example 1.
[0031] FIG. 7 shows the test results illustrating the specific
surface area of the beads obtained according to Test Example 1.
[0032] FIG. 8 shows the test results illustrating the expansion
degree of the beads obtained according to Test Example 1 after
injecting dinitrogen gas.
DETAILED DESCRIPTION
[0033] The present disclosure relates to a method for preparing a
carrier including ammonium oxidizing bacteria immobilized therein
and a method for improving the gas permeability and strength of the
carrier.
[0034] The ammonium oxidizing bacteria immobilized in the carrier
disclosed herein may comprise at least one selected from a group
comprising anaerobic ammonium oxidizing bacteria and aerobic
ammonium oxidizing bacteria. Particularly, the ammonium oxidizing
bacteria may be anaerobic ammonium oxidizing bacteria or aerobic
ammonium oxidizing bacteria.
[0035] Alternatively, heterotrophic denitrifying bacteria can be
used instead of the ammonium oxidizing bacteria in order to remove
nitrite or nitrate in the form of dinitrogen gas through a
heterotrophic denitrification.
[0036] Anaerobic ammonium oxidizing bacteria remove nitrogen in
sewage and wastewater through anaerobic ammonium oxidation
(Chemical Formula 1), while aerobic ammonium oxidizing bacteria
remove ammoniacal nitrogen in sewage and wastewater through
nitrification (Chemical Formula 2) and partial nitrification
(Chemical Formula 3).
1NH.sub.4.sub.++1.32NO.sub.2.sub.-+0.066HCO.sub.3.sub.-+0.13H+.fwdarw.1.-
02N.sub.2.+0.26NO.sub.3.sub.-+0.066CH.sub.2O.sub.0.5N.sub.0.15.+2.03H.sub.-
2O [Chemical Formula 1]
NH.sub.4.sub.++1.5O.sub.2.fwdarw.NO.sub.2.sub.-+H.sub.2O+2H+
[Chemical Formula 2]
NH.sub.4.sub.++0.75O.sub.2+HCO.sub.3.sub.-.fwdarw.0.5NH.sub.4.sub.++0.5N-
O.sub.2.sub.-+CO.sub.2+1.5H.sub.2O
2NO.sub.3.sub.-+10H++10e-.fwdarw.N.sub.2+2OH-+4H.sub.2O
2NO.sub.2.sub.-+6H+6e-.fwdarw.N.sub.2+2OH-+2H.sub.2O [Chemical
Formula 3]
[0037] Hereinafter, the carrier including ammonium oxidizing
bacteria immobilized therein and the method for preparing the same
according to an embodiment of the present disclosure will be
explained in more detail with reference to the accompanying
drawings.
[0038] Referring to FIG. 1, a PVA-alginate mixed solution and
sludge are prepared individually.
[0039] The PVA-alginate mixed solution is one containing polyvinyl
alcohol (PVA) mixed with alginate in distilled water (S101). A
solution including a mixture of 10-20 g of PVA and 1-5 g of sodium
alginate per 100 g of distilled water may be used. To accomplish
homogeneous mixing of PVA with alginate, the PVA-alginate mixed
solution may be dissolved at a temperature of 100.degree. C. or
higher for a predetermined time.
[0040] The sludge means one containing ammonium oxidizing bacteria,
wherein the ammonium oxidizing bacteria may comprise at least one
selected from a group comprising anaerobic ammonium oxidizing
bacteria and aerobic ammonium oxidizing bacteria. Alternatively,
heterotrophic denitrifying bacteria can be used instead of the
ammonium oxidizing bacteria in order to remove nitrite or nitrate
in the form of dinitrogen gas through a heterotrophic
denitrification.
[0041] To improve the biological activity of the prepared beads,
highly concentrated sludge may be used and such highly concentrated
sludge may be prepared through gravity precipitation and
centrifugal separation. In addition, to increase the amount of
anaerobic ammonium oxidizing bacteria supported at first, the
concentration of volatile suspended solids (VSS) in the sludge may
be increased to 5-10 VSS g/L. In addition to this, the sludge may
be screened with a sieve having a size of 100-1,000 .mu.m to obtain
a uniform size of bacteria.
[0042] Then, the PVA-alginate mixed solution is mixed with the
sludge. The PVA-alginate mixed solution and the sludge may be mixed
at a volume ratio of 1:1-4.
[0043] After mixing the PVA-alginate mixed solution with the
sludge, sodium bicarbonate (NaHCO.sub.3) is further introduced and
mixed again (S102). Sodium bicarbonate (NaHCO.sub.3) is an
inorganic foaming agent and is decomposed under an environment of
pH 3-4 to produce carbon dioxide (CO.sub.2). Such carbon dioxide
(CO.sub.2) produced by the decomposition of sodium bicarbonate
(NaHCO.sub.3) functions to form pores in the beads during the
formation of the beads. Hereinafter, the solution in which the
PVA-alginate mixed solution, sludge and sodium bicarbonate
(NaHCO.sub.3) are mixed is referred to as `foaming-beading
solution`. Meanwhile, zeolite may be further introduced to the
foaming-beading solution for the purpose of controlling the
specific gravity of the beads.
[0044] After the solution in which the PVA-alginate mixed solution,
sludge and sodium bicarbonate (NaHCO.sub.3) are mixed, i.e., the
foaming-beading solution is prepared, the viscous foaming-beading
solution is dropped to a saturated boric acid (H.sub.3BO.sub.3)
solution containing calcium chloride (CaCl.sub.2). Herein,
saturated boric acid (H.sub.3BO.sub.3) and calcium chloride
(CaCl.sub.2) are crosslinking agents for converting the
foaming-beading solution into beads. Calcium chloride functions as
a crosslinking agent for alginate, while saturated boric acid
functions as a crosslinking agent for PVA. Saturated boric acid
(H.sub.3BO.sub.3) solution contains 0.5-1 g of calcium chloride
(CaCl.sub.2) per 100 g of distilled water.
[0045] As the foaming-beading solution is dropped to saturated
boric acid (H.sub.3BO.sub.3) containing calcium chloride
(CaCl.sub.2), PVA is crosslinked with alginate to form beads, and
the sludge is supported in the beads and immobilized therein
(S103). For reference, FIG. 2 is a schematic view illustrating the
method for preparing a carrier including ammonium oxidizing
bacteria immobilized therein according to an embodiment of the
present disclosure.
[0046] During the formation of the beads, sodium bicarbonate
(NaHCO.sub.3) contained in the foaming-beading solution is
decomposed to produce carbon dioxide (CO.sub.2). Such carbon
dioxide (CO.sub.2) produced by the decomposition of sodium
bicarbonate (NaHCO.sub.3) is discharged to the exterior of the
beads. As carbon dioxide (CO.sub.2) in the beads is discharged to
the exterior of the beads, pores are formed in the beads.
[0047] When the finished beads are used to culture ammonium
oxidizing bacteria or the ammonium oxidizing bacteria are used to
treat sewage and wastewater, the ammonium oxidizing bacteria, such
as anaerobic ammonium oxidizing bacteria in the beads grow with
ammonium and nitrite as substrates and produce dinitrogen gas
(N.sub.2). When dinitrogen gas in the beads is not discharged to
the exterior, beads are swelled undesirably. To allow effective
discharge of dinitrogen gas, it is required that a dinitrogen gas
flow path is provided in the beads. According to an embodiment,
sodium bicarbonate (NaHCO.sub.3) as an inorganic foaming agent is
used to form pores functioning as a dinitrogen gas flow path in the
beads. The pores functions not only as a dinitrogen gas flow path
but also as a path through which dissolved oxygen is supplied into
the beads during nitrification.
[0048] Meanwhile, decomposition of sodium bicarbonate (NaHCO.sub.3)
into carbon dioxide (CO.sub.2) is carried out under an environment
of pH 3-4. Thus, it is required that the saturated boric acid
(H.sub.3BO.sub.3) solution containing calcium chloride (CaCl.sub.2)
is controlled to have pH 3-4.
[0049] As mentioned above, sodium bicarbonate (NaHCO.sub.3) as an
inorganic foaming agent functions to form pores in the beads. Use
of inorganic foaming agents other than sodium bicarbonate
(NaHCO.sub.3), such as calcium carbonate (CaCO.sub.3) or sodium
carbonate (Na.sub.2CO.sub.3), may be considered. However, in the
case of calcium carbonate (CaCO.sub.3), it has a significantly low
solubility of about 1.3-1.5 mg to 100 g of distilled water, and
thus is hardly dissolved in the foaming-beading solution. Although
it may be dissolved at a very low pH condition (1 or less), such a
severely low pH condition adversely affects the activity of
bacteria. In addition, in the case of sodium carbonate
(Na.sub.2CO.sub.3), spherical pores are not formed during the
conversion into beads and individual aggregation is poor to cause
agglomeration of beads among themselves. Thus, it is difficult to
obtain beads, i.e., carrier, having a diameter of 3-7 mm.
[0050] Therefore, it is required to use sodium bicarbonate
(NaHCO.sub.3) to form pores stably while not adversely affecting
the activity of bacteria. In addition, sodium bicarbonate
(NaHCO.sub.3) not only functions to form pores in the beads but
also functions to improve the strength of beads. Improvement of the
strength of beads accomplished by sodium bicarbonate (NaHCO.sub.3)
is supported by the following test results as described hereinafter
in detail. To satisfy both formation of pores in the beads and
improvement of strength of beads, it is required to introduce
sodium bicarbonate (NaHCO.sub.3) to the foaming-beading solution in
an amount of 0.15-1.2% (w/v), particularly 0.5-0.7% (w/v), as
described hereinafter in detail with reference to the test
results.
[0051] Hereinabove, formation of beads in the beads using sodium
bicarbonate (NaHCO.sub.3) is suggested. However, pore formation may
be carried out by using solid particles. A method for forming pores
using solid particles will be explained hereinafter.
[0052] When the formation of beads is finished while solid
particles are incorporated to the foaming-beading solution, the
solid particles form no chemical bonding with PVA or alginate, and
thus are detached from the beads by external physical impact having
a predetermined intensity. Then, pores connecting the inner part of
the beads with the outer part thereof are formed at the portions
where the solid particles are detached. Herein, the term "physical
impact having a predetermined intensity" means the contact among
beads caused by the action of an agitator or external physical
impact for detaching the solid particles from the beads.
[0053] The solid particles may be added to and mixed with the
foaming-beading solution, or may be mixed preliminarily with the
PVA-alginate mixed solution. In addition, the solid particles may
include any materials which do not chemically react with PVA and
alginate. According to an embodiment, activated carbon having a
size of 10 .mu.m-1 mm or less is used. Further, the solid particles
are mixed at a ratio of 0.5-5 g per 100 g of distilled water, based
on the case where the solid particles are mixed with the
PVA-alginate mixed solution. When the amount of the solid particles
in the PVA-alginate mixed solution is larger than 5%, beads are not
formed due to an increase in viscosity caused by the solid
particles.
[0054] As methods for forming pores, use of sodium bicarbonate
(NaHCO.sub.3) and use of solid particles are suggested. The two
methods may be applied individually or in combination.
[0055] Meanwhile, when the foaming-beading solution is dropped to
the saturated boric acid (H.sub.3BO.sub.3) solution containing
calcium chloride (CaCl.sub.2) to form beads including the sludge
immobilized therein, the size of beads may be controlled
considering the reaction efficiency of ammonium oxidizing bacteria,
or the like. A smaller size of beads provides higher reaction
efficiency of ammonium oxidizing bacteria. However, the bead size
may be about 1-7 mm in order to prevent leakage of the beads from
the reactor. The bead size may be controlled by using a needle,
tube or funnel optionally. It is possible to control the mechanical
strength through the reaction time between the foaming-beading
solution and saturated boric acid solution.
[0056] In addition, when the foaming-beading solution is dropped to
the saturated boric acid (H.sub.3BO.sub.3) solution containing
calcium chloride (CaCl.sub.2) to form beads including the sludge
immobilized therein, the foaming-beading solution may be maintained
at a temperature of 30-50.degree. C. When the beads are required to
have a much smaller size, the temperature of the foaming-beading
solution may be controlled to 70.degree. C. to reduce the
viscosity.
[0057] After the foaming-beading solution is dropped to the
saturated boric acid (H.sub.3BO.sub.3) solution containing calcium
chloride (CaCl.sub.2) to form beads including the sludge
immobilized therein, the beads are dipped in 0.5-1 M phosphoric
acid (KH.sub.2PO.sub.4) solution to further reinforce the
mechanical strength of the beads (S104).
[0058] Then, the beads are washed with distilled water 2-3 times,
and dipped in distilled water to cause swelling (S105). Through the
swelling, sodium bicarbonate (NaHCO.sub.3) and unreacted alginate
remaining in the beads are discharged to the exterior. In this
manner, the method for preparing a carrier including ammonium
oxidizing bacteria immobilized therein is completed.
[0059] Hereinabove, the carrier including ammonium oxidizing
bacteria immobilized therein and the method for preparing the same
according to an embodiment are described. Hereinafter, the present
disclosure will be explained in more detail with reference to
Examples.
Example 1: Preparation of Carrier
[0060] First, 15 g of PVA and 2 g of sodium alginate are mixed per
100 g of distilled water to provide a PVA-alginate mixed solution.
Next, sludge containing anaerobic ammonium oxidizing bacteria is
added to the PVA-alginate mixed solution. Then, sodium bicarbonate
(NaHCO.sub.3) is introduced to the PVA-alginate mixed solution
mixed with sludge in an amount of 0, 0.15, 0.30, 0.60 or 1.20%
(w/v) to provide foaming-beading solutions. After that, each
foaming-beading solution is dropped to a saturated boric acid
solution containing 0.5-1 g of calcium chloride per 100 g of
distilled water to form beads. The beads are allowed to react with
0.5M phosphoric acid solution.
Example 2: Pores and Swelling Property of Carrier
[0061] FIG. 3 is a scanning electron microscopic (SEM) image of the
beads obtained according to Example 1. As shown in FIG. 3, in the
case of the beads to which no sodium bicarbonate (NaHCO.sub.3) is
introduced (see, `control` in FIG. 3), pores are little formed as
compared to the beads to which sodium bicarbonate (NaHCO.sub.3) is
introduced. In addition, as the amount of sodium bicarbonate
(NaHCO.sub.3) is increased, pore size is increased, as also
determined by the porosity test results as shown in FIG. 4.
Referring to FIG. 4, as the amount of sodium bicarbonate
(NaHCO.sub.3) is increased, porosity is increased.
[0062] Meanwhile, after measuring the density of the beads obtained
according to Example 1, it can be seen that the density of the
beads is increased as the amount of sodium bicarbonate
(NaHCO.sub.3) is increased up to 0.3% (w/v) as shown in FIG. 5.
However, when the amount of sodium bicarbonate (NaHCO.sub.3) is
higher than 0.3% (w/v), the density of the beads is decreased. It
is thought that this is because the swelling degree is different
depending on the amount of sodium bicarbonate (NaHCO.sub.3).
[0063] Referring to FIG. 6, it can be seen that when the amount of
sodium bicarbonate (NaHCO.sub.3) is within a range of 0-0.3% (w/v),
a higher amount of sodium bicarbonate (NaHCO.sub.3) increases the
amount of pores formed inside and outside of the beads, and thus
the contact of boric acid solution with the PVA and alginate inside
and outside of the beads is improved, resulting in a decrease in
swelling degree. On the contrary, it is thought that when the
amount of sodium bicarbonate (NaHCO.sub.3) is higher than 0.6%
(w/v), the swelling degree is increased due to the pores formed
additionally.
[0064] It can be seen from the results of FIG. 4-FIG. 6,
introduction of sodium bicarbonate (NaHCO.sub.3) improves the
porous property of the beads. In addition, referring to the results
of FIG. 5 and FIG. 6, the density of the beads is increased and the
swelling degree of the beads is decreased until the amount of
sodium bicarbonate (NaHCO.sub.3) is up to 0.3% (w/v). This is
because sodium bicarbonate (NaHCO.sub.3) introduced to the beads
causes increased formation of pores and the pores improve the
contact property of the boric acid solution with PVA and alginate
inside and outside of the beads, resulting in formation of beads
with a dense structure. However, when the amount of sodium
bicarbonate (NaHCO.sub.3) is higher than 0.6% (w/v), the opposite
result is obtained. It is thought that this results from
additionally formed pores. When the amount of sodium bicarbonate
(NaHCO.sub.3) is higher than 0.6% (w/v), there is a similar
tendency of improvement in contact with the boric acid caused by
pore formation.
[0065] Therefore, it can be seen from the above results that
introduction of sodium bicarbonate (NaHCO.sub.3) improves the
contact of boric acid solution with PVA and alginate inside and
outside of the beads, and thus increases the strength of the
beads.
[0066] Meanwhile, the tendency of density and swelling degree as
shown in FIG. 5 and FIG. 6 conforms to the tendency of specific
surface area as shown in FIG. 7. Referring to FIG. 7, the specific
surface area of the beads is decreased as the amount of sodium
bicarbonate (NaHCO.sub.3) up to 0.3% (w/v) and is increased at a
higher amount.
Example 3: Gas Permeability
[0067] The beads obtained according to Example 1 are subjected to a
gas permeability test.
[0068] First, dinitrogen gas is injected to each type of beads
obtained according to Example 1 at a flow rate of 1 L N.sub.2/min.
For reference, when treating highly concentrated wastewater by
using anaerobic ammonium oxidizing bacteria, the flow rate of
dinitrogen gas produced by the anaerobic ammonium oxidizing
bacteria is about 0.44 L N.sub.2/min.
[0069] Referring to FIG. 8, in the case of the beads to which no
sodium bicarbonate (NaHCO.sub.3) is introduced, the beads have a
diameter of 4.49 mm before the injection of dinitrogen gas.
However, after the injection of dinitrogen gas, the beads are
swelled to a diameter of 13.5 mm and are broken finally. On the
contrary, when sodium bicarbonate (NaHCO.sub.3) is introduced, the
swelling degree of the beads is decreased as the amount of the
sodium bicarbonate (NaHCO.sub.3) introduced thereto is increased.
When the amount of dinitrogen gas is 0.3% (w/v) or higher, the
beads show an insignificant difference in diameter before and after
the injection of dinitrogen gas. This suggests that dinitrogen gas
in the beads is discharged effectively.
Example 4: Nitrogen Removal Property
[0070] To a reactor filled with influent, the beads obtained
according to Example 1 are introduced and each type of beads is
examined for nitrogen removal rate.
[0071] The operating conditions of the reactor are shown in the
following Table 1 and the composition of the influent is shown in
the following Table 2. In addition, the nitrogen removal rate (NRR)
results of each type of beads depending on nitrogen loading rate
(NLR) are shown in the following Table 3.
TABLE-US-00001 TABLE 1 Operating Conditions of Reactor Reactor
volume 280 mL Packing ratio 42.7% Agitation speed 350 rpm Hydraulic
retention time 8 hrs
TABLE-US-00002 TABLE 2 Composition of Influent NH.sub.4.sub.+--N
50, 100, 150, 200, 300, 500 mg/L NO.sub.2.sub.---N 50, 100, 150,
200, 300, 500 mg/L HCO.sub.3.sub.- 72 mg/L KH.sub.2PO.sub.4 6 mg/L
MgCl.cndot.6H.sub.2O 12 mg/L CaCl.sub.2.cndot.2H.sub.2O 48 mg/L
Trace I, II 1 mL/L
TABLE-US-00003 TABLE 3 Nitrogen Removal Rate (NRR) of Each Type of
Beads Depending on Nitrogen Loading Rate (NLR) Period NLR NRR (kg
N/m.sup.3/d) Stage (day) (kg N/m.sup.3/d) Control 0.30 % (w/v) 0.60
% (w/v) 1.20 % (v/w) 1 0-28 0.23 .+-. 0.03 0.10 .+-. 0.05 0.11 .+-.
0.05 0.11 .+-. 0.05 0.11 .+-. 0.05 2 29-36 0.32 .+-. 0.04 0.30 .+-.
0.05 0.30 .+-. 0.05 0.27 .+-. 0.07 0.07 .+-. 0.05 3 37-48 0.61 .+-.
0.01 0.54 .+-. 0.03 0.55 .+-. 0.05 0.55 .+-. 0.03 -- 4 49-66 0.91
.+-. 0.02 0.82 .+-. 0.03 0.83 .+-. 0.03 0.83 .+-. 0.03 -- 5 67-75
1.19 .+-. 0.02 1.04 .+-. 0.03 1.05 .+-. 0.02 1.08 .+-. 0.03 -- 6
76-83 1.81 .+-. 0.01 1.67 .+-. 0.01 1.67 .+-. 0.01 1.69 .+-. 0.02
-- 7 84-86 3.11 .+-. 0.01 1.93 .+-. 0.08 1.81 .+-. 0.02 2.25 .+-.
0.03 -- 8 86-120 3.15 .+-. 0.01 1.00 .+-. 0.03 1.79 .+-. 0.02 2.75
.+-. 0.03
[0072] Referring to Table 3, in the case of the beads (see,
"control" in Table 3) to which no sodium bicarbonate (NaHCO.sub.3)
is introduced, the nitrogen removal rate is reduced rapidly at the
point of 86 days after the operation. After operating for 120 days,
it can be seen that most of the beads are swelled or broken by
nitrogen produced during the operation.
[0073] On the contrary, when the amount of sodium bicarbonate
(NaHCO.sub.3) is 0.3% or 0.6%, a higher nitrogen removal rate than
that of "control" is obtained. Particularly, when the amount of
sodium bicarbonate (NaHCO.sub.3) is 0.6%, a very high nitrogen
removal rate of 2.75 kgN/m.sup.3/d or lower is obtained. Meanwhile,
when the amount is 1.2%, no activity is shown due to the loss of
bacteria after the reactor is operated for 36 days.
[0074] Based on the above results, it can be seen that when the
amount of sodium bicarbonate (NaHCO.sub.3) is 0.6%, particularly
0.5-0.7%, the highest nitrogen removal rate is obtained.
* * * * *